Exclusion and Inclusion of Nonwhite Ethnic Minority Groups in 72 North American and European Cardiovascular Cohort Studies

Background: Cohort studies are recommended for understanding ethnic disparities in cardiovascular disease. Our objective was to review the process for identifying, including, and excluding ethnic minority populations in published cardiovascular cohort studies in Europe and North America. Methods and Findings: We found the literature using Medline (1966–2005), Embase (1980–2001), Cinahl, Web of Science, and citations from references; consultations with colleagues; Internet searches; and RB's personal files. A total of 72 studies were included, 39 starting after 1975. Decision-making on inclusion and exclusion of racial/ethnic groups, the conceptual basis of race/ethnicity, and methods of classification of racial/ethnic groups were rarely explicit. Few publications provided details on the racial/ethnic composition of the study setting or sample, and 39 gave no description. Several studies were located in small towns or in occupational settings, where ethnic minority populations are underrepresented. Studies on general populations usually had too few participants for analysis by race/ethnicity. Eight studies were explicitly on Caucasians/whites, and two excluded ethnic minority groups from the whole or part of the study on the basis of language or birthplace criteria. Ten studies were designed to compare white and nonwhite populations, while five studies focused on one nonwhite racial/ethnic group; all 15 of these were performed in the US. Conclusions: There is a shortage of information from cardiovascular cohort studies on racial/ethnic minority populations, although this has recently changed in the US. There is, particularly in Europe, an inequity resulting from a lack of research data in nonwhite populations. Urgent action is now required in Europe to address this disparity. A systematic review reveals a shortage of information on racial and ethnic minority populations. This compromises the relevance of the evidence underlying health policies and guidelines for nonwhite patients. Background: As a result of migration, mostly for economic reasons, populations in many countries around the world are becoming increasingly diverse. In many cases, ethnic minorities differ in their socio-economic circumstances, culture, lifestyle, and genetic make-up from the majority population (and there are, of course, also differences within the majority group and within minority groups). These differences in risk factors (such as diet and smoking) can influence a person's susceptibility to disease. For some diseases, such as heart disease, it is well known that particular ethnic groups are at higher risk than others. It is not always clear, though, whether this high risk is due to socio-economic circumstances, culture, genes, lifestyle, or a combination of these factors. Why Was This Study Done?: Cardiovascular disease, which can cause heart attacks and strokes, is the most common cause of death in the US and most European countries. Rates of cardiovascular diseases vary substantially between different countries, and also between different ethnic groups in ethnically diverse countries such as the UK and the US. Researchers and health policy makers need to understand more about the variations in cardiovascular disease. To ensure the best possible health care for the entire population, they need to know how exactly the risks differ between different ethnic groups and what causes those differences. One key research tool to address these questions are so-called cohort studies (a cohort refers to a specific group of people that are studied over time). Cohort studies are “forward looking”—they typically enroll a large number of healthy participants who are then followed over a number or years to study long-term health outcomes. Over the past decades, a number of cohort studies have focused on cardiovascular disease. In this study, researchers wanted to find out whether these cohort studies included or excluded ethnic minority groups. What Did the Researchers Do and Find?: They searched the medical literature for cohort studies on cardiovascular disease. They found 72 that met their criteria and analyzed them in detail. The researchers discovered that most of the cohort studies did not provide detailed information on the ethnic composition of the broader populations from which the participants were recruited. Most of them also did not state whether minority groups were included in or excluded from the study. Additionally, the researchers found that many of the studies did not give details on the ethnic composition of the participants themselves, or on how the participants' ethnicity was determined. Studies with participants that were representative of diverse populations usually were not large enough to answer the kinds of questions necessary to determine differences between different ethnic groups. However, ten of the studies were designed specifically to compare white and nonwhite participants, and five studies focused on nonwhite minority groups specifically. All 15 of those studies were done in the US. What Does This Mean?: Despite the knowledge that ethnicity matters in cardiovascular disease, most cohort studies have not been designed to further explore this connection. The situation in the US seems to be changing, with a number of recent studies designed to add data on cardiovascular disease risks and causes among minority populations. No such studies have yet been reported in Europe. Research strategies in Europe should be adjusted to meet this need. Where Can I Find More Information Online?: The following Web sites provide information on minority participation in health research.